The present invention relates generally to rotary heat exchangers and, more specifically, to an improved radial sealing assembly for use between relatively rotatable parts of a rotary regenerative heat exchanger.
In a typical rotary regenerative heat exchanger, such as a rotary air preheater, a cylindrical rotor is disposed about a central rotor post and divided into a plurality of sector-shaped compartments by a plurality of radial partitions extending from the rotor post to the outer shell of the rotor. A mass of heat absorbent material commonly comprised of packed plate-like elements is carried in each of the sector-shaped compartments of the rotor. As the rotor is rotated about the central axis of the rotor post, heat absorbent material is alternately exposed to a stream of a heating gas and then upon further rotation of the rotor to a stream of cooler air or other gas to be heated. As the heat absorbent material is exposed to the heating gas, it absorbs heat therefrom and when exposed to the cool air or other gas to be heated, the heat absorbed from the heating gas by the heat absorbent material is transferred to the cooler air or gas. The rotor is surrounded by a housing including end plates at opposite ends thereof having flow impervious portions located between circumferentially spaced openings that provide for the flow of the heating gas and the gas to be heated through the rotor. To prevent mingling of the heating gas with the air or other gas to be heated, the radial partitions that form the rotor compartments are provided with radial sealing members along their edges to wipe against the flow impervious portions of the end plates as the rotor rotates thereby providing a sealing relationship.
In a typical rotary regenerative heat exchanger, such as an air preheater, the heating gas, hereinafter referred to as the hot gas, and the gas to be heated, hereinafter referred to as cold air, enter the rotor shell from opposite ends and pass in opposite directions over the heat exchange material housed within the rotor. Thus, the cold air inlet and the cooled gas outlet are at one end of the heat exchanger housing, commonly referred to as the cold end, while the hot gas inlet and the heated air outlet are at the opposite ends of the heat exchanger housing, commonly referred to as the hot end. As a result of this inlet and outlet configuration, an axial temperature variation exists within the rotor shell from the hot end of the rotor to the cold end of the rotor. In response to this thermal gradient, the rotor tends to distort. As a result, the radial seals mounted on the radial partitions at the hot end of the rotor are pulled away from the end plates of the housing adjacent thereto with the greater separation occurring at the outboard end of the rotor. This opens a gap which if not closed would allow flow therethrough resulting in an undesired intermingling of the gas and the air.
In the typical prior art air preheater, the radial seals were formed of rigid leaves extending along the end edge of the radial partitions so as to bridge the gap between the end surface of the radial partition and the confronting face of the end plates of the housing. As this rigid sealing leaf would pull away from the end plate at the hot end of the rotor as described hereinbefore, various schemes were developed for reestablishing contact between the seal leaves mounted to the radial partitions and the end plates. For example, in U.S. Pat. Nos. 3,786,868, 4,124,063 and 4,206,803, the end plate at the hot end physcially distorts to recontact the radial seals mounted to the radial partitions. In U.S. Pat. Nos. 3,095,036, 3,166,119, and 3,189,084, the seal leaves themselves are slidably mounted to the radial partitions so as to be physically movable back into contact with the end plates despite the turn down of the rotor. However, in either arrangement, monitoring and control systems must be provided to ensure that the recontacting of the radial seals with the end plates of the housing takes place in such a manner as not to crush the radial seals.
One proposed solution to this problem is to provide a flexible sealing member between the radial partition and the end plate of the rotor housing. This has been done by mounting flexible metallic strips to the radially outward end of the rigid leaves so that the flexible strips extend outwardly from the rigid leaf to contact the end plate of the rotor housing. The rigid leaf is in turn attached to the radial plate in a conventional manner. The flexible metallic strips will maintain their rigidity under the small pressure differential, typically less than 5 p.s.i., existing between the air and gas streams flowing through the rotor but will flex when the end plates and sealing strips are brought into contact when adjusting for rotor distortion, thereby avoiding damage to the seal leaves while allowing a sealing relationship to be established between the radial partitions and the end plates of the rotor housing.
However, it has been experienced that these relatively thin flexible metallic sealing strips are frequently damaged and ripped off during the soot blowing of the heat transfer element to remove particulates therefrom. It is customary, and periodically necessary, to clean the heat transfer material within the rotor by delivering a blast of high pressure air or steam, typically at about 200 p.s.i., from soot blowers through the passages in the heat transfer material to dislodge any particulate deposits from the surface thereof and carry them away leaving a relatively clean surface and open flow passages in order to maintain the efficiency of the air heater. Unfortunately, the force of the high pressure blowing medium on the relatively thin, flexible sealing strips causes the sealing strips to bend backward frequently resulting in stresses within the sealing strips beyond the yield point of the material from which the flexible sealing strips are formed thereby causing a permanent deformation of the sealing strips which reduce their sealing effectiveness and, after repeated soot blowings, cracking the sealing strips and resulting in a complete loss of the sealing structure.
It is, therefore, an object of the present invention to provide an improved radial sealing assembly wherein flexible sealing strips are provided but the yielding of the sealing strips under the soot blowing pressure is precluded.